1. Field of the Invention
This invention relates to thickened aqueous surfactant solutions as well as the use of such solutions in cosmetic preparations of the type used in the field of personal hygiene such as hair shampoos, foam baths, shower baths, handwashing pastes and the like.
2. Statement of the Related Art
Surfactant solution mixtures generally are formulated to contain anionic surfactants, such as alkyl ether sulfates, as the principal surfactant component. Thickeners are normally added to such solutions to stabilize the clear or disperse systems and to improve the handling properties. Many compounds are known as agents for increasing the viscosity of formulations containing anionic surfactants. The most simple and inexpensive means for regulating the viscosity of solutions containing anionic surfactants is to add sodium chloride or other inorganic water-soluble electrolyte salts. In addition to or instead of these inorganic components, it is also known to add soluble organic compounds having a thickening effect. Thus, it is known that fatty acid alkanolamides, such as coconut oil fatty acid monoethanolamide, lauric acid monoethanolamide, oleic acid diethanolamide and coconut oil fatty acid diethanolamide, have a thickening effect on many surfactant systems and increase the foam stability of the systems in the presence of fats. In addition, it is known that polyethylene glycol difatty acid esters and many water soluble polymers also have a thickening effect on aqueous surfactant solutions.
However, many thickeners such as recited above are attended by numerous disadvantages. Solutions thickened with polyethylene glycol fatty acid diester often show inadequate viscosity stability during storage and water-soluble polymers are often difficult to dissolve and may give rise to unwanted, slimy flow behavior with a tendency towards "stringing", which is highly undesirable in cosmetic preparations. Derivatives of diethanolamine such as fatty acid alkanolamides are increasingly undesirable in cosmetic preparations because they often contain a small content of free alkanolamine as a byproduct or impurity, which can give rise to the formation of nitrosamines.